1. Field of the Invention
This invention relates to gypsum boards having improved adhesion between the gypsum core and paper facers and to a method for manufacturing the same.
2. Description of the Prior Art
Typically, in the manufacture of gypsum board, a liquid foam is added to the board core slurry mix to replace a portion of the more expensive components of the core and thereby produce a lighter, easier to handle board. In the process, the foamed slurry of calcined gypsum is continuously deposited on a moving fibrous sheet which constitutes one cover for the final product. A second cover sheet is then applied on top of the slurry to form a sandwich which passes through a forming station which determines the width and thickness of the gypsum board.
A strong bond must be provided between the gypsum core and the paper covering sheets in the finished panel to prevent the separation or delamination of the paper from the core. Without a sufficiently strong bond, various environmental conditions can adversely impact the boards. For example, even a very brief exposure to high humidities can cause a weakening at or near the paper core interface and result in damage during storage and use of the boards. Various attempts have been made over the years to improve the paper-gypsum bond. One such attempt is disclosed in White U.S. Pat. No. 4,327,146 wherein, during the final processing steps in the paper manufacturing plant, a defoaming agent is applied to the paper surface which becomes the covering paper's inner face in the gypsum board. The thus manufactured paper is then transferred to the gypsum board manufacturing plant for use in producing the paper-covered gypsum board.